Preferably, medical dairy products are highly concentrated in nutrients, in particular in proteins and minerals, to meet the daily intake of nutrients in malnourished patients. These patients can be cachectic patients or persons suffering from end-stage AIDS, cancer or cancer treatment, severe pulmonary diseases like COPD (chronic obstructive pulmonary disease), tuberculosis and other infection diseases or persons that experienced severe surgery or trauma like burns. Furthermore, persons suffering from disorders in the throat or mouth such as oesophageal cancer or stomatitis and persons having problems with swallowing like dysphagic persons, require special liquid, low-volume nutrition. Also, persons just suffering from reduced appetite or loss of taste, will benefit from low-volume, preferably liquid, food. These patients can also be elderly persons, in particular frail elderly and elderly at risk of becoming frail. In this regard, although an elderly person's energy needs may be reduced, their ability to consume products may also be diminished. For example, they may have difficulty consuming a product due to, e.g., swallowing difficulties, or due to too large amount of product they need to consume to meet the daily intake of nutrients. Hence, compliance is not optimal, and often, the intake is suboptimal, leading to suboptimal nourishment, and in the end, to malnutrition.
The aforementioned groups of patients may be extremely sensitive to food consistency and to the organoleptic properties of the product such as, for instance viscosity, mouth feel, taste, smell and colour. Also, patients such as cachectic patients, typically suffer from extreme weakness which often prevents them from sitting in a vertical position and from drinking food from a carton or even to suck it from a straw. These patients benefit well from liquid low-volume enteral compositions with a high content of nutrients, in particular proteins.
However, high amounts of protein and minerals increase the overall viscosity of the product during processing and storage because of shifts in the protein-mineral equilibria. Low viscous liquid products, however, are mostly appreciated by patients, which makes it challenging to formulate such products.
Therefore, the problem underlying the present invention is to provide a liquid enteral composition for providing nutrition, either as a supplement, or as a complete nutrition, comprising a high content of an intact protein, in particular micellar casein, as major protein source, in the smallest volume of liquid, and which supports nutrition and well-being in the different patient groups mentioned above, in particular to an elderly person or an ill patient.
Casein micelles in concentrated milk interact more frequently with each other than in bovine milk because of the smaller distances between the micelles. Concentrated milk, therefore, behaves like a shear-thinning non-Newtonian fluid, which means that viscosity is dependent on shear rate (Karlsson et al., 2005). The viscosity of colloidal systems is, in general, dependent of the viscosity of the continuous phase, shape, and size distribution of particles, and of their mutual interactions together with assumptions on how the viscosity follows the volume fraction. The volume fraction (Φ) of the casein micelles is a dimensionless number, defined as fraction of the total volume taken by the particles. It can be determined by measuring the viscosity (η) of the solution. Eilers (1945) generated formula (1) to estimate the viscosity of concentrated dairy systems.
                    η        =                                            η              0                        ⁡                          (                              1                +                                                      1.25                    ⁢                    Φ                                                        1                    -                                          Φ                      /                                              Φ                        max                                                                                                        )                                2                                    (        1        )            η0 represents the viscosity of the continuous phase and is 1 mPa·s. Φmax represents the maximum packing volume fraction for which the viscosity tends to go to infinity. A value of 0.74 is normally used for Φmax in a solution with spheres of similar sizes (Eilers, 1945), but for concentrated milk, in which the particles have various sizes, a value of 0.79 should be used. This formula is extended from the Einstein relation, which describes the viscosity of dispersions in very dilute systems, in which the particles are spherical and not deformable or affected by each other's presence (Dewan et al., 1972; Eilers, 1945; Karlsson et al., 2005).
Voluminosity is defined as the total volume occupied by a gram of protein and has been related to the volume fraction Φ of the proteins in the solution (Eilers, 1941) The voluminosity of the casein micelles is a determining factor for the viscosity of the solution. The voluminosity of casein micelles increases when the micelles become more hydrated (e.g. due to calcium depletion), which causes release of specific caseins from the micelle and expansion and swelling of the micelles. The order of specific casein release depends on the amount of phosphoserine residues and hence the specific sensitivity for calcium ions. When the micelles become more calcium depleted, more casein will be released from the casein micelle. As a result, the order of dissociation is β-casein>αs1-casein>αs2-casein (Holt, 1997). Although κ-casein has 0 or 1 phosphoserine residues, it will probably remain stacked into the casein micelle because of its hydrophobic interactions. For instance, the amount of β-casein that leaves the casein micelles increases with decreasing temperature and calcium content. The increase in size of the casein micelles is caused by expansion and swelling of the casein micelles, which is due to increase in electrostatic repulsion and osmosis of continuous phase in the micelles, respectively (Leviton and Pallansch, 1962). Moreover, the free calcium ions in the continuous phase reduce the electrostatic repulsion in the casein micelles, which keeps the micelles more compact.
The interactions between casein micelles in concentrated milk are strongly influenced by e.g. ionic strength, mineral content and composition, pH, and temperature (Karlsson et al., 2005). Phosphates and citrate, which are minerals that are frequently added to medical nutrition, processed cheese, or (concentrated) UHT milk, interact with casein micelles by binding calcium ions or by binding directly to the casein micelle (Kocak and Zadow, 1985; Mizuno and Lucey, 2005; Vujicic et al., 1968). In general, their calcium binding capacity can be ranked in the following order: long-chain phosphate > tripolyphosphate > pyrophosphate > citrate > orthophosphate (Zittle, 1966).